High-performance planing monohull sailboat with heeling control

ABSTRACT

A sailboat which uses hydrofoils either immersed or planning on the water&#39;s surface to resist heeling. The boat uses two hydrofoil assemblies, one for the starboard side of the boat and one for its port side. Each part can generate either positive or negative lift. The attack angles and depths of immersion of each hydrofoil are adjustable. The struts which hold the hydrofoils are designed so that the leeway forces produced by the struts are much lower than the lifts produced by the hydrofoils so there is little or no conflict between the hydrodynamic force produced by the hydrofoil and its supporting strut.

TECHNICAL FIELD

Monohull sailing vessels using hydrofoils and increasing the speed andstability of such vessels.

Objective

The objective of the boat is to provide a monohull sailboat which has asubstantially greater speed and stability than current monohullsailboats. It (1) enables the use of sails with much larger areas thancommon sailboats, in some cases larger by a factor of two or more, (2)constrains heeling to low angles, (3) enhances planning and (4) providesa boat with greater stability in a larger range of sailing conditionsthan usual. In addition the apparatus used to control heel can alsoreduce the apparent weight of the boat, thereby decreasing displacementand skin friction drags, which then increases boat speed.

A further objective of the boat is to use dual purpose foils which canact as both hydrofoils and planning boards and provide smooth adjustmentover a wide range of operating conditions. Yet another objective is toprovide boats which combine performance advantages of both monohulls andcatamarans.

BACKGROUND

It is well known to those familiar with the art that heeling reduces thespeed and stability of a sailboat, and if heeling exceeds certainlimits, the boat can capsize. Heeling produces several phenomena whichreduce the speed of the boat. Most importantly, the effective area ofthe sail is reduced to the product of actual area and the cosine of theheel angle. For small heel angles this effect is small, but at heelangles over 20° it is substantial.

Also the hull of a boat is designed to produce the least drag when theboat is upright or almost upright. In addition boats with lightweighthulls will suffer from additional heeling if the heeling angle is largeenough that the weight of the sail, rigging and spars contribute toheeling.

To counteract heeling monohulls are often equipped with deep, heavykeels, sometimes cantilevered to increase anti-heeling. However, as windspeed increases, heeling forces increase, but the anti-heeling forcedoes not, so eventually the boat will capsize.

Multi-hull boats use hulls wide apart to counter heeling, but thisresults in vessels which do not tack easily and are often more difficultto moor and dock.

It is also known to those practiced in the art that there is a maximumspeed, which is call the “displacement speed,” “critical speed” or “hullspeed,” at which monohull sailboats can travel. This value varies as thesquare root of the length of the boat at the waterline, and therefore ismuch smaller for small boats than for large ones. As wind speedincreases and critical speed is approached, using larger sail area haslittle or no effect.

Using hulls designed to plane allows critical speed to be exceeded, butoften the result is not substantial. If monohulls are equipped withenough sail to plane at low wind speed, they generally heel excessivelyin moderate winds and are prone to capsizing.

It is well known that if hydrofoils are used to inhibit heeling and ifthe hydrofoils are outwardly canted, the hydrodynamic forces produced bythe hydrofoils and those produced by their supporting strut oppose eachother, thereby reducing the heeling suppression force. Outwardly cantedhydrofoils can be used on a monohull if the opposing force problem isavoided by allowing the strut to self-align to the leeway angleestablished by the daggerboard or keel or to be manually set by the creweach time the boat comes about. However self-alignment increases thecomplexity and cost of the boat and manual operation is ofteninconvenient, particularly for single-handed boats.

To combat heeling due to propeller torque or uneven weight distributionon motor boats, planning foils, called trim tabs, are sometimes mountedon the stern. One is tilted up and the other down to rotate the boat inthe opposite direction of the undesired heel. This heeling suppressiontechnique would be less effective on sailboats because the boat's sternis generally narrow, limiting the lever arm available.

Foils which have historically been used for heeling suppression havebeen either submerged or at the surface of the water in the planningmode, but not used both ways.

The design of the current boat avoids the disadvantages of priortechniques and combines the most useful features of several of them.

PRIOR ART

Ketterman

Ketterman, in his college dissertation, Senior Project Trifoiler,determined that if hydrofoils are canted outward, the hydrodynamicforces generated by vertical struts, which on catamarans determine theleeway angle the boat travels at and the forces generated by horizontalhydrofoils used to lift the boat conflict with each other.

Welbourn

Welbourn, U.S. Pat. No. 7,644,672, describes means of counteractingheeling by use of a laterally translatable hydrofoil which is mounted inthe hull of a boat, provides positive lift, and can be moved from thewindward side of a boat to its leeward side and vice versa. In thissituation, leeway angle issue is not a concern because there are nostruts.

Coffman

Coffman, US Patent Application 20110259254, covers an apparatus whichconverts a monohull into a trifoiler at a wind speed sufficient to causethe boat to be foil borne.

SUMMARY

The boat described herein is intended to overcome the performance andcost constraints of previous techniques and combines the advantages ofseveral of them.

The boat employs one or more outwardly canted hydrofoils on both thestarboard and port sides of the boat. The hydrofoils can be adjusted forattack angle and depth of immersion enabling a wide range ofanti-heeling action correction and can act either as ordinary hydrofoilsor planning foils.

The struts holding the hydrofoils are designed to reduce or eliminatethe conflict of hydrodynamic forces which normally reduces theeffectiveness of outwardly canted hydrofoils. Furthermore, the immersedarea of a strut is kept small compared to the area of the hydrofoilattached to it, on the order of 10% of the hydrofoil area or less innormal operation.

Unlike other heeling suppression techniques used on keel boats andcatamarans, as wind and boat speed increase, heeling suppressionautomatically increases using the techniques described herein. Thisdramatically reduces the probability of capsizing.

The hydrofoil apparatus increases the stability of sailboats partly byincreasing the apparent beam of the boat.

The apparatus can be employed by monohull sailboats of various sizes. Itcan be incorporated during manufacture or as an accessory to existingboats.

Many of the methods of increasing the speed of sailboats function bestin a narrow range of wind speeds. For instance when a catamaran becomesfoil borne, its speed increases significantly, but below that hydrofoilsoffer little advantage. Thus adding hydrofoils to a catamaran is mostuseful only at high winds, and, in general, in most parts of the world,consistently high winds are rare. Because the boat described hereinrelies on a very large sail(s) to provide extra speed, its benefits areevident at all wind velocities. Particularly good results have beenmeasured at low to moderate speeds.

Recently development has been done on the use of hydrofoils on sailboatsto combat heeling. Early work was done by Ketterman who studied inwardlyand outwardly canted hydrofoils on catamarans. His analysis proved thatif the struts holding the hydrofoil contribute to setting the leewayangle, the hydrodynamic forces produced by the hydrofoil and the strutoppose each other if the hydrofoil is outwardly canted. Thisconsideration is particularly important in catamaran or trimaran designswhich rely exclusively on the struts setting the leeway angle.

The boat described herein can be used in the hydrofoil, planning orhybrid mode and in some embodiments smoothly transforms without skipperintervention from one to the other as wind ebbs and flows and the boat'sheel lessens or increases. In some embodiments the apparatus can bealtered by the crew from one mode to the other or adjusted in attackangle and/or depth of immersion to increase or decrease the anti-heelingforce.

In most operating modes the leeway force produced by the strut is small(preferably 10% or less) as compared to the positive lifting force ofthe hydrofoil. In many embodiments this accomplished by making thesubmerged area of the vertical strut which holds a hydrofoil muchsmaller than the submerged area of the hydrofoil so that the conflictbetween the lifting and leeway producing forces is minimized.

In one embodiment, the boat, shown in FIG. 1, is equipped with twoanti-heeling apparatuses near the daggerboard well, one on the starboardside and one on the port side. An outwardly canted hydrofoil can beplaced in each assembly. Each can be operated separately over a range ofpossible attack angle positions—to produce negative lift or positivelift or no lift. As viewed from starboard, for negative lift thehydrofoil is rotated clockwise with respect to an upright position, andfor positive lift it is rotated counterclockwise. The device which holdsa hydrofoil is aligned with the center line of the boat. The hydrofoilscan be raised or lowered in the apparatuses.

A hydrofoil can operate in lifting mode or in the planning mode or canbe raised above the water level, where it performs neither function.Either, both or neither hydrofoil can be set to engage the water. Howmuch a hydrofoil engages the water depends on how far it is lowered,which is determined by how much heeling suppression force is desired.

DRAWINGS

FIG. 1 is a three dimensional view of a high performance planingmonohull sailboat with heeling control suppression apparatuses mountedon the hull.

FIG. 2 is a front view of the high performance planing monohull sailboatwith heeling control.

FIG. 3 is a three dimensional view of the high performance planingmonohull sailboat with heeling control with a Marconi rig.

FIG. 4 is a front view of the high performance planing monohull sailboatwith heeling control with the hydrofoils removed.

FIG. 5 a is a front view of the high performance planing monohullsailboat with heeling control showing operation of the boat in lightwinds.

FIG. 5 b is a front view of the high performance planing monohullsailboat with heeling control showing operation of the boat andreduction of the apparent weight of the boat.

FIG. 6 is a front view of the high performance planing monohull sailboatwith heeling control showing operation of the boat in moderate winds.

FIG. 7 is a front view of the high performance planing monohull sailboatwith heeling control showing the operation of the boat in strong winds.

FIG. 8 is a front view of the high performance planing monohull sailboatwith heeling control showing the hydrofoil positions when running andreaching.

FIG. 9 is a front view of the high performance planing monohull sailboatwith heeling control showing the hydrofoils in position to improve boatstability.

FIG. 10 is a three dimensional view of a hydrofoil for use with the highperformance planing monohull sailboat with heeling control.

FIG. 11 is a three dimensional view of a typical strut for use with thehigh performance planing monohull sailboat with heeling control.

FIG. 12 is a three dimensional view of a hydrofoil assembly, i.e., thecombination of a hydrofoil and a strut, for use with high performanceplaning monohull sailboat with heeling control.

FIG. 13 is a three dimensional view of a hydrofoil assembly holder foruse with the high performance planing monohull sailboat with heelingcontrol.

FIG. 14 is a three dimensional view of a hull for use with the highperformance planing monohull sailboat with heeling control.

FIG. 15 is a three dimensional view of details of the hull of the highperformance planing monohull sailboat with heeling control where thehydrofoil are mounted.

FIG. 16 is a three dimensional view of a hydrofoil apparatus, includingthe hydrofoil assembly and hydrofoil assembly holder, mounted to thehull of the high performance planing monohull sailboat with heelingcontrol.

FIG. 17 is a side view of a sailboat having a lateen rig.

FIG. 18 is a side view of a typical daggerboard for use with the highperformance planing monohull sailboat with heeling control.

FIG. 19 is a side view of a typical rudder for use with the highperformance planing monohull sailboat with heeling control.

FIG. 20 a is a side view of the hydrofoil apparatus of the highperformance planing monohull sailboat with heeling control showing thehydrofoil set at an attack angle of zero.

FIG. 20 b is a side view of the hydrofoil apparatus of the highperformance planning monohull sailboat with heeling control showing thehydrofoil set an attack angle of plus twelve degrees.

FIG. 20 c is a side view of the hydrofoil apparatus of the highperformance planning monohull sailboat with heeling control showing thehydrofoil set an attack angle of minus twelve degrees.

FIG. 21 is a perspective view of hydrofoil apparatus of the highperformance planning monohull sailboat with heeling control showing aclamp which can be used to adjust and lock the vertical position of thestrut.

FIGS. 22 a and 22 b illustrate an embodiment in which the hydrofoilapparatuses can be rotated into a stowed position.

OPERATION OF THE INVENTION

Referring to FIG. 1 an apparatus, 1-1, is positioned on the starboardside of the boat, and another, 1-2, on the port side. These apparatusesare also shown in FIG. 2, which is the view of the boat from the front.FIG. 3 shows an embodiment which differs for the one in FIG. 1 by usinga different sail shape. The details in FIG. 2 would apply to eitherconfiguration.

Very Low Speed Wind

Note in FIG. 2 that the hydrofoils, 2-1, are above the water level, 2-2,and the struts, 2-3, are fully up. The attack angles of the hydrofoilsare set a 0 in the figure, but can be varied. The zero attack angle isdenoted by the “0”, 2-4.

In this figure and other figures referred to in this section, ahorizontal arrow, 2-5 shows wind direction, and if the hydrofoilsproduced any lift, either positive or negative, it would be shown by oneof the arrows, 2-6, aimed up or down. The angle, 2-7, of the bottom ofthe boat with respect to the waterline in this embodiment isapproximately 10°, flat enough to enable planning.

If the crew can know for certain that the wind will stay low enough thatthe skipper hiking out can hold the boat level or nearly level, then hemay opt to go sailing without the hydrofoils as shown in FIG. 4.

In very low winds the heel, if any, is controlled by the position of thecrew, or in the case of single-handed operation, by the position of theskipper. Normally the skipper does not choose to sail the boat in aperfectly upright position. If the boat is on a beat or reach, the boatsails heeling slightly to leeward so that gravity causes the sail totake a smooth camber rather than to wrinkle up. A smooth camber causesair to flow smoothly across the sail which, increases the power of thesail. If the boat is on a run, it is usually heeled slightly to windwardso the center of force on the sail is directly over the centerline ofthe boat. This prevents the force on the sail from trying to rotate theboat, i.e., to produce a weather helm. A weather helm must be opposed bya force on the tiller, and that force increases rudder drag.

Low Wind Speed

At low wind speeds heeling is countered both by the skipper hiking outand the actions of the hydrofoils.

This situation is illustrated in FIGS. 5 a & b. The wind, 5 a-1, causesthe boat to heel to leeward in this case by an angle equal to the anglethe hydrofoil, 5 a-2, makes with the deck, the same angle the bottom ofthe boat also makes with the deck. This situation facilitates planning.

The angle of the heel is determined by the position of the skipperhiking to windward, the force of the wind, and the lift, 5 a-3, of theleeward hydrofoil, 5 a-2. The attack angle is set positive as shown bythe plus sign, 5 a-4. The windward hydrofoil, 5 a-5, is out of the waterand is set at a zero attack angle, 5 a-6.

As the wind increases, the boat speeds up and the lift, 5 b-1, of theleeward hydrofoil increases as shown in FIG. 5 b. A similar effect inconstant wind may be obtained by increasing the attack angle of theleeward hydrofoil while decreasing the righting moment of the skipper.In either situation, the apparent weight of the boat is reduced as shownby the change in water level, 5 b-2, on the hull, 5 b-3. Under theseconditions the leeward hydrofoil may be in the planning mode with theleading edge of the foil out of water and the trailing edge riding onthe water. A rule of thumb states that the lift of a foil in theplanning mode is about one third that of the foil in the hydrofoil mode,so as the boat speeds up, the lift reaches a new equilibrium at a valuesomewhere between that of a deeply immersed hydrofoil and a planningfoil.

Moderate Wind Speed

At moderate wind speeds, the skipper hikes out further than at lowerwind speeds and/or uses a larger leeward foil attack angle to maintainthe boat at the desired heeling angle. However, eventually, as windspeed increases, these adjustments cannot overcome the heeling force.

When this occurs, the windward foil is lowered so it engages the wateras shown in FIG. 6. The foil is lowered, and the negative attack angleis increased just enough so enough righting force is produced tosupplement the righting force of the skipper hiking out and the rightingforce of the leeward foil so that the boat is brought to an acceptableheeling angle. In this situation, the struts, 6-1 and 6-2, have aminimal area under water so the conflict between hydrodynamic forcesproduced by the struts and the foils is not significant. The leewayangle is set by the daggerboard, 6-3.

In moderate winds expert sailors may be able to adjust the immersiondepths and attack angles of the windward and leeward hydrofoils so thatthe leeward foil operates in the planning mode and the windward oneproduces a normal hydrofoil action. This would result in a minimumapparent boat weight.

If a sudden and intense puff is encountered, the skipper can quicklylower the windward hydrofoil if it has been previously set at a negativeattack angle, but is not fully engaged with the water.

High Wind Speed

When the wind is strong, both hydrofoils are generally deeply immersedand set at high attack angles, the windward one negative and the leewardone positive. The depths of immersion are chosen so that the hydrofoilsdo not suffer significantly from loss of power due to being too near thewater surface yet not deep enough to cause the foils and the struts toproduce significant conflicting hydrodynamic forces. If maximum liftingforces from both hydrofoils are not needed, the leeward one is set toproduce the greater force in order to lower the apparent weight of theboat and reduce displacement and skin friction drags. The apparentweight of the boat is its true weight less the net positive lift of thehydrofoils. Typical settings are shown in FIG. 7.

In this figure it is seen that on the leeward side, the vector, 7-1,representing the sideways force produced by the hydrofoil pushes theboat to leeward, while on the windward side it, 7-2, pushes the boat towindward. In some cases it is possible balance these two forces so thehydrofoils do not affect to the leeway angle.

Running and Broad Reaching

FIG. 8 shows the positions of the hydrofoils when the boat is running oron a broad reach. The coordinates, 8-1, of the image and thecoordinates, 8-2, of the space in which the boat is sailing areillustrated. The z axis is the direction of the boat. In the windvector, 8-3, can be resolved into a vector, 8-4, denoting the windcoming from directly aft and a vector, 8-5, representing the windathwartships. In this example the beam component is small so the heelingforce is also. Since the heeling force is negligibly small, the positionof the skipper and the settings of the hydrofoils can cause the boat totake any heeling angle desired. With the wind directly or almostdirectly from aft, if the boat is perfectly vertical, the center offorce on the sail is to leeward of the centerline of the boat so will beforced to rotate into the wind, i.e., exhibit a weather helm. This wouldput pressure on the rudder and generate induced drag.

But if the boat is heeled to windward, the center of force can be placeddirectly over the boat's centerline, eliminating the weather helm. Asshown in the figure, the boom, 8-6, extends to leeward and the boatheels to windward. This situation results from the positions of the twohydrofoils which are acting as planning foils. If change in wind speedcauses the boat of change the heeling angle, one or the other planningfoil will exhibit increased lift opposing any further change in heeling.The if a strong puff causes a sharp increase in heeling angle, theleeward foil will dip much further into the water, which converts itsheeling action from planning to hydrofoiling, a change which ultimatelyincreases lifting force by a factor of three. As the boat rights, thelifting force decreases because the foil approaches the water surfaceuntil a new equilibrium is reached.

Improved Stability

FIG. 9 illustrates how the hydrofoils are set if the goal is tostabilize the boat in light winds rather than to combat heeling, asmight be the case if a youngster is learning to sail using the boatdescribed herein. Instability is inherent to a boat which has unusuallylarge sail area so means to improve stability can be very useful.

The foil settings used for improved stability in light airs are similarto those used for running. Both foils are set at positive lift anglesand normally operate in the planning mode. The value of the attack angledepends on the amount of stability desired, with larger angle producinggreater stability.

Another feature of the boat is the ability to use the drags of thehydrofoils to combat weather or lee helms. If the boat's trim producesexcessive weather helm, some compensation can be obtained by relyingmore on the leeward hydrofoil for righting moment than on the windwardone.

Design

The design of the boat is analyzed by starting with the hydrofoilbecause its performance influences all aspects of the boat.

FIG. 10 shows a preferred embodiment of a starboard hydrofoil. The part,10-1, which extends out to the right, is the section of the hydrofoilwhich generates most of the lift. Its cross section is similar to anaircraft's wing. It is cambered on the top and flat at the bottom sothat it provides the best lift at a positive attack angle. However, itwill produce negative lift at attack angles greater than a few negativedegrees. In the preferred embodiment, the angle of attack can vary from−12 to +12 degrees. The base of the hydrofoil, 10-2, is flat on the topso it provides an easy surface for the attachment of the strut. The topsurface also interfaces smoothly with the bottom of the hydrofoilapparatus when the strut is pull completely up. The hydrofoil assemblyconsists of a hydrofoil and strut.

The strut, 11-1, in FIG. 11 has flat sides so it slides smoothly in thehydrofoil assembly holder and fits snugly front to back in the holder.The strut has a hand-hold, 11-2, near the top. The bottom of the strut,11-3, mates with the top of the base, 10-2, of the hydrofoil. In someembodiments the hydrofoil can be detached from the strut and can bereplaced by hydrofoils of various designs if less or more lift isdesired for the prevailing weather conditions.

FIG. 12 shows the hydrofoil attached to the strut to fon n the hydrofoilassembly, 12-1. This assembly is raised or lowered to adjust the depthof immersion of the hydrofoil. If the wind is very light and thehydrofoils are not needed to enhance boat stability, the boat can be puton its side and the hydrofoil assembly can be slid out the bottom of theboat and stored.

Laterally the angle of the hydrofoil with respect to horizontal is theangle A, 12-2. In the preferred embodiment it is same angle each side ofthe bottom makes with the deck, an arrangement which enhances planningwhen the boat heels at this angle.

FIG. 13 illustrates the hydrofoil assembly holder, 13-1. The holderallows the hydrofoil assembly to slide up and down to adjust hydrofoilimmersion depth. It pivots around a pin or hub attached to the boat toadjust attack angle. The hole, 13-2, for this pin is in the lowerright-hand corner of the holder. In the preferred embodiment the outsidevertical surfaces, 13-3, of the holder are lined with a sheet of Teflonor similar low friction material to facilitate adjusting the attackangle. There is a hole through hydrofoil holder assembly which containsrod, 13-4. This rod extends through slots, 20 a-11, in the sides of theapparatus and in the preferred embodiment is part of a cam clamp whichlocks the attack angle of the hydrofoil. The lengths of the slotsdetermine the range of attack angles possible as seen in FIG. 20 a.

The hydrofoil assembly holder mounts on the hull of the boat. The hullwithout the hydrofoil assembly holders is shown in FIG. 14. Being about14 feet long, the hull is similar to that of a Sunfish® except that thebeam is about 8 inches wider, and the transom, 14-1, is also wider toenhance hiking. There is a slot, 14-2, for the daggerboard. The mast isinserted in the step, 14-4. There is a cockpit, 14-5 for the skipper'sfeet. The sections, 14-6, of the freeboard just behind the positions ofthe hydrofoil apparatuses are parallel to the boat's center line so thatwater splashing from the hydrofoils does not get on the deck. There is ahole, 14-7, which goes through the outer freeboard, 14-8, and is in linewith a hole in inner freeboard, 14-6. These holes are used for the pinwhich mounts the hydrofoil assembly holder in place.

The hull is fabricated from Kevlar and carbon fiber textiles, or similarmaterials. Kelvar is puncture resistant and carbon fiber textiles arestrong and stiff. The result is a light-weight, durable hull.

Details of the parts of the hydrofoil apparatus which are parts of thehull are shown in FIG. 15. The outer part, 15-1, of the apparatus is anextension of the front section of the freeboard. 15-2. The inner part,15-3, is molded into or otherwise permanently affixed to the aft sectionof the freeboard, 15-4. The hole, 15-5, is where the pin goes whichholds the hydrofoil assembly holder in place. This hole extends throughboth the outer and inner parts of the apparatus and terminated in athreaded blind insert at the inner part. There are slots, 15-6, in theboth the inner and outer parts which hold the hydrofoil assembly holderat the attack angle when the apparatus is fully assembled.

FIG. 16 shows the apparatus assembled with its hydrofoil assemblyholder, 16-1, hydrofoil assembly, 16-2, and pivot pin, 16-3. The pivotpin is passed through the apparatus parts affixed to the hull and thehydrofoil assembly holder and screwed into the blind, threaded insert inthe in board side of the apparatus. In the preferred embodiment, a camclamp, 16-4, is used to lock the attack angle.

When in use, any positive or negative lifting force produced by thehydrofoil passes from the hydrofoil assembly to the hydrofoil assemblyholder and then to the hull. The design of the apparatus allows thehydrofoil assembly holder to be varied over the attack angle adjustmentrange.

The hydrofoil assembly, 16-2, is inserted upward through the slot in thehydrofoil assembly holder.

Several other parts of the boat are shown in FIGS. 17, 18, and 19. Thesail, 17-1, for a typical embodiment is illustrated in FIG. 17. It hasan area of approximately 150 square feet, twice that of a Laser orSunfish® sail. The sail shown is a lateen rig. This rig is employedbecause it uses a long boom, which keeps the center or force lower thana Marconi rig. The low center of force helps to reduce heeling moment.However, the Marconi rig shown in FIG. 3 will allow the boat to pointhigher. The head, 17-2, of sail is approximately 23 feet above the deck.The hull, 17-3, is approximately 14 feet long, almost the same as Laser,420 or Sunfish®. The sail area is double that of comparable sized boats,and since the force generated by the sail varies directly with sail areawhile displacement and skin friction drags vary as the square of boatspeed, all other factors being equal, the boat will go about 40% fasterthan the comparable other boats. If the boat is operated such that thenet force of the hydrofoils is positive, the speed advantage may be evenlarger since the boat rides higher. This effect is somewhat offset bythe drags generated by the hydrofoils.

The boat's daggerboard, 18-1, is shown in FIG. 18. Its length is aboutfive feet, somewhat longer than boats of comparable size. The longerdaggerboard is needed to facilitate righting a capsized boat by standingon its tip. The daggerboard contains a hand-hold, 18-2, a hole, 18-3 forbungee to hold it in place, if elevated, and a stop, 18-4, to prevent itfrom falling out.

A typical rudder, 19-1, appears in FIG. 19. In the preferred embodimentthe rudder is a pop-up type suitable for beaching and is attached to theboat by a gudgeon and pintle arrangement which is familiar to thosepracticed in the art. The rudder is long and narrow. Length is importantbecause in the planning mode, the boat rises up on the water, and itsnarrowness is beneficial because the center of force of its horizontallift (known as a weather helm) is near the transom so provides a largemechanical advantage for the tiller, 19-2, minimizing the pressure onthe helm. This is particularly important on a boat with a lateen rigbecause if the gooseneck is far forward, the weather helm can beconsiderable.

Because the boat permits adjustment of both attack angle and depth ofimmersion, the skipper may have many adjustments to perform whentacking. In addition to operating the tiller and the sheet, he canadjust the attack angles and immersion depths of both hydrofoils. Hemust keep one hand on the tiller at all times so all the adjustmentsordinarily must be made with one hand. The adjustments of the hydrofoilsare made to optimize the amount and polarity of lift (positive ornegative). When the hydrofoil is below water level but near the surfaceof the water, lift can be varied over a wide range from zero to themaximum possible for the attack angle chosen by changing the depth ofimmersion. And, if the attack angle is set at maximum, there is littleusefulness to backing down on attack angle since nearly the entire rangeof lift can be selected by changing foil depth. Thus the number ofadjustments can be reduced merely by using only the maximum attackangle.

Alternatively if the foil is keep nearly at full depth, changingimmersion has little effect so changing lift can be accomplished bychanging attack angle only. Using either strategy, the number ofadjustments needed for ordinary hydrofoil operation can be cut in half.Another approach to making adjustments easier involves using theskipper's feet to adjust settings.

Ordinarily in light airs using fixed attack angles and varying onlyimmersion depth is useful, while in heavy weather it is best to fix thedepth of immersion and vary the attack angle. In any case, the boat isdesigned so all four possible adjustments may use either fixed orvariable settings.

The operation of the equipment used to adjust attack angle can beexamined by studying FIGS. 20 a,b &c, which describe three possiblesettings and their effects on the function of the hydrofoils. FIG. 20 ashows the apparatus when set at 0 degrees attack angle. The hydrofoil isset slightly below its stowed position. It must be lowered slightlybecause in the stowed position, the hydrofoil butts up against thebottom of the apparatus.

In these figures solid lines, 20 a-1, delineate parts which would beseen by an observer. Dark dotted lines, 20 a-2, show parts of thehydrofoil assembly obscured by other parts of the apparatus, and lightdotted lines, 20 a-3, show obscured parts of the hydrofoil assemblyholder. The very dark dotted line, 20 a-4, is the surface of the water,and the water itself is the area with slanted dotted lines.

The arrow, 20 a-5, shows the direction of boat travel.

The chine, 20 a-6, is slightly above the water level, 20 a-4.

The pivot point, 20 a-7, for the hydrofoil holder assembly is the pointabout which the holder changes its angle to set the attack angle. In thepreferred embodiment a cam clamp is used to lock the attack angle. Thereare a large number of techniques, know to those practiced in the art,which can be used to lock the attack angle and depth of immersion,including vliers, travelers and pins. In the preferred embodiment, theshaft, 20 a-8, of a cam clamp passes through the outer freeboard, 20a-9, then through the hydrofoil assembly holder, and ends at the innerfreeboard 20 a-10. The shaft passes through a hole in the hydrofoilassembly holder. It moves in slots, 20 a-11, in the two freeboards asattack angle is altered, and the hydrofoil assembly holder rotates. Whenthe cam on end of the shaft in depressed, it pulls the outer freeboardtoward the inner one securing the hydrofoil assembly holder in thechosen position. Because the end of the shaft at the inner freeboardmust slide in its slot, there is a mechanism in the hull which providesit this freedom. The details of the operation of a cam clamp arefamiliar to those skilled in the art.

The pivot point hardware consists of a stainless steel bolt, threaded atthe end which feeds into a blind threaded insert mounted in the innerfreeboard. The entire interior of the apparatus can be removed frombetween the inner and outer freeboards by removing the bolt.

FIGS. 20 b and 20 c illustrate the positions of the hydrofoil assemblyat the ends of the attack angle adjustment range, i.e., +12 and −12degrees. In both figures the hydrofoil assembly has been further loweredso it engages the water. For clarity a simplified, miniature drawing, 20b-1, is included.

FIG. 20 b shows the hydrofoil is set for maximum positive lift, 20 b-3,and FIG. 20 c is for maximum negative lift, 20 c-1. In both figures thelevel of the water is for the position at the edge of the cambered partof the hydrofoil toward the hull. Since the hydrofoil makes an angle of10 degrees to the water surface, the situation describing the engagementof hydrofoil with the water varies with distance from the hull. In thefigures it is clear that the outer tip of the hydrofoil, 20 b-2, isabove the surface of the water. The black dot, 20 b-4, shows theposition of the shaft on the cam clamp which is used to fix the attackangle. Cam clamps are available athttp://www.rockler.com/clamps/cam-clamps or can be custom designed. Oneof the advantages of using cam clamps to set attack angle and immersiondepth is that the handles can be used for manually altering position aswell as for locking down.

When the hydrofoil in FIG. 20 b is lowered, it converts from theplanning mode to the hydrofoiling mode, ultimately producing a liftingforce of about three times that in the planning mode. When the hydrofoilin FIG. 20 c is lowered, it converts a skimming mode to a hydrofoil modeand attains maximum negative lift when it reaches its lowest position.

FIG. 21 describes the hydrofoil assembly holder with the hydrofoilassembly inserted and shows a cam clamp which locks the strut in placevertically. The strut, 21-1, has been inserted into the hydrofoil holderassembly, 21-2. The clamping mechanism consists of a block, 21-3, and acam clamp, 21-4. To change the immersion depth of the hydrofoil, thelever on the cam clamp is pulled back which releases the pressure on theback edge of the strut allowing the strut to move. When the strut is inthe correct position the lever is then pushed forward, pressing theblock against the strut.

EMBODIMENTS

Embodiments of the boat can take a variety of forms, depending on sizeof boat and performance desired.

In various embodiments the dimensions and shapes of the hydrofoil andstrut may differ. The maximum depth of immersion, the range of attackangles, the shape and camber of the hydrofoil, and the canting angle ofthe hydrofoil can take various values.

Means of changing the angle of attack, altering the hydrofoils depth ofimmersion, and holding the angle of attack and depth of immersionconstant can take differing of forms. The adjustment of the angle ofattack and depth of immersion can be manual or mechanized.

Various sail plans including plans utilizing jibs and spinnakers can bethe utilized as can various hull designs including flat and curvedbottoms. All these possibilities are well known to those familiar withthe art.

In one embodiment of the invention two hydrofoil apparatuses are placedon each side of the boat. This arrangement is particularly appropriatefor use by children who are just learning to sail since it improves thestability of the boat and diminishes the possibility of pitch-poling.

Embodiments which use various strut designs are helpful in somesituations. For instance in high wind situations in which the hydrofoilsare deeply immersed, and the conflict between the hydrodynamic forces ofthe hydrofoil and the strut becomes significant, an embodiment could usetwo rods instead of a flat strut. Also the lateral lift coefficient ofthe strut can be reduced in embodiments which have rough surfaces orslots to upset laminar flow around the strut.

An embodiment is possible in which the position of the boom—to leewardor to windward—determines whether the attack angle in positive ornegative. This simplifies the task of manually setting the attack angle.

Having the hydrofoils increase the effective beam of the boat may bedisadvantageous when the boat is operated in crowded fleets or harbors,and would make approaching a dock more difficult. An embodiment whichallows the hydrofoil apparatus to rotate onto the deck or backwardtoward the stern addresses this issue as shown in FIG. 22. The drawingshows the apparatus mounted on a Sunfish® hull, 22 a-1. The mountingbrackets, 22 b-1 has been permanently affixed to the hull. There is ahinge, 22 b-3, on each mounting bracket, and each hinge is affixed to ahydrofoil apparatus as well as to the mounting bracket. The pivot point,22 a-2, is the center of rotation of the hinge. FIG. 22 b shows theapparatuses in the stowed position, while FIG. 22 a illustrates theapparatus ready for sailing. Also using pairs of hydrofoil apparatuseson each side of the boat reduces the effective beam by allowing shorterhydrofoils.

When the boat heels, a sidewise force is generated in addition to theusual upward or downward lift. In another embodiment means of adjustingthe angle of the strut to hold it vertical can be utilized.

1. A sailboat, comprising: a. a hull, b. at least two hydrofoilapparatuses, one or more on the starboard side of the hull and one ormore on the port side of the hull, c. wherein each hydrofoil apparatusis configured to adjustably hold a hydrofoil assembly, d. wherein eachhydrofoil assembly comprises a strut and a hydrofoil, e. the strut andthe hydrofoil each having an area intended to contact water, f. whereinthe leeway force produced by the strut is small in comparison to thelifting force of hydrofoil, and g. the hydrofoils are outwardly cantedwith respect to the hull.
 2. The sailboat of claim 1, wherein eachhydrofoil apparatus is configured to adjustably hold a hydrofoilassembly in at least two positions.
 3. The sailboat of claim 1, whereineach strut is oriented vertically and each hydrofoil is orientedhorizontally.
 4. The sailboat of claim 1, wherein each strut is orientedapproximately vertically and each hydrofoil is oriented approximatelyhorizontally.
 5. The sailboat of claim 2, wherein each of the outwardlycanted hydrofoils can be positioned to plane on the surface of thewater.
 6. The sailboat of claim 2, wherein each of the outwardly cantedhydrofoils can be positioned to be immersed in the water.
 7. Thesailboat of claim 5, wherein each of the outwardly canted hydrofoils canbe positioned to be immersed in the water.
 8. The sailboat of claim 1,where the hydrofoil apparatuses are configured to resist heeling of thesailboat.
 9. The sailboat of claim 2, wherein the hydrofoil apparatusare configured to adjustably hold the hydrofoils in a positive liftposition.
 10. The sailboat of claim 2, wherein the hydrofoil apparatusare configured to adjustably hold the hydrofoils in a negative liftposition.
 11. The sailboat of claim 9, wherein the hydrofoil apparatusare configured to adjustably hold the hydrofoils in a negative liftposition.
 12. The sailboat of claim 2, wherein each hydrofoil apparatusis configured to adjustably hold the hydrofoils in at least two verticalpositions.
 13. The sailboat of claim 1, wherein the struts have an areacontacting the water that is much less than that of the area of thehydrofoils contacting the water so that the struts do not generatehydrodynamic forces which conflict with the lifting forces of thehydrofoils during operation of the sailboat.
 14. The sailboat of claim1, wherein the leeway force produced by the strut is 10% or less thanthe lifting force of the hydrofoil.
 15. The sailboat of claim 1, whereinthe leeway force produced by the strut is 5% or less than the liftingforce of the hydrofoil.
 16. The sailboat of claim 13, wherein the areaof the strut contacting the water is 10% or less than the area of thehydrofoil contacting the water.
 17. The sailboat of claim 13, whereinthe area of the strut contacting the water is 5% or less than the areaof the hydrofoil contacting the water.
 18. Two or more hydrofoilapparatuses configured to be mounted to a sailboat hull, comprising: a.each hydrofoil apparatus configured to adjustably hold a hydrofoilassembly, b. wherein each hydrofoil assembly comprises a strut and ahydrofoil, c. the strut and the hydrofoil each having an area intendedto contact water, d. wherein the leeway force produced by the strut issmall in comparison to the positive force of hydrofoil, and e. thehydrofoils are configured to be outwardly canted with respect to thesailboat hull.
 19. The apparatuses of claim 18, wherein each hydrofoilapparatus is configured to adjustably hold a hydrofoil assembly in atleast two positions.
 20. The apparatuses of claim 18, wherein each strutis oriented vertically and each hydrofoil is oriented horizontally. 21.The apparatuses of claim 18, wherein each strut is orientedapproximately vertically and each hydrofoil is oriented approximatelyhorizontally.
 22. The apparatuses of claim 20, wherein each of theoutwardly canted hydrofoils can be positioned to plane on the surface ofthe water.
 23. The apparatuses of claim 20, wherein each of theoutwardly canted hydrofoils can be positioned to be immersed in thewater.
 24. The apparatuses of claim 22, wherein each of the outwardlycanted hydrofoils can be positioned to be immersed in the water.
 25. Theapparatuses of claim 18, where the hydrofoil apparatuses are configuredto resist heeling of the sailboat.
 26. The apparatuses of claim 19,wherein the hydrofoil apparatus are configured to adjustably hold thehydrofoils in a positive lift position.
 27. The apparatuses of claim 19,wherein the hydrofoil apparatus are configured to adjustably hold thehydrofoils in a negative lift position.
 28. The apparatuses of claim 26,wherein the hydrofoil apparatus are configured to adjustably hold thehydrofoils in a negative lift position.
 29. The apparatuses of claim 19,wherein each hydrofoil apparatus is configured to adjustably hold thehydrofoils in at least two vertical positions.
 30. The apparatuses ofclaim 18, wherein the struts have an area contacting the water that ismuch less than that of the area of the hydrofoils contacting the waterso that the struts do not generate hydrodynamic forces which conflictwith the lifting forces of the hydrofoils during operation of thesailboat.
 31. The sailboat of claim 18, wherein the leeway forceproduced by the strut is 10% or less than the lifting force of thehydrofoil.
 32. The sailboat of claim 18, wherein the leeway forceproduced by the strut is 5% or less than the lifting force of thehydrofoil.
 33. The sailboat of claim 30, wherein the area of the strutcontacting the water is 10% less than the area of the hydrofoilcontacting the water.
 34. The sailboat of claim 30, wherein the area ofthe strut contacting the water is 5% less than the area of the hydrofoilcontacting the water.